Ultrafine mixed-crystal oxide, production process and use thereof

ABSTRACT

A process for producing an ultrafine mixed-crystal oxide characterized by producing an ultrafine mixed crystal oxide comprising primary particles in a mixed crystal state with a BET specific surface area of 10 to 200 m 2 /g, comprising the step of subjecting a halogenated metal to high temperature oxidation with an oxidizing gas to produce a metal oxide by a vapor phase production method, wherein said halogenated metal is in the form of a mixed gas (a mixed halogenated metal gas) comprising at least two compounds having a different metal elements selected from the group consisting of chlorides, bromides, and iodides of titanium, silicon, and aluminum, and said mixed halogenated metal gas and said oxidizing gas are independently preheated to 500° C. or more prior to a reaction, a ultrafine mixed crystal oxide obtained by the process, and use of the oxide.

CROSS-REFERENCE TO RELATED APPLICATION

This is a divisional of application Ser. No. 09/775,549 filed Feb. 5,2001, now U.S. Pat. No. 6,572,964 which claims benefit of ProvisionalApplication No. 60/214,426 filed Jun. 28, 2000; the above noted priorapplications are all hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to an ultrafine mixed-crystal oxideobtained by a vapor phase method, and the production process thereof.More specifically, the present invention relates to an ultrafinemixed-crystal oxide with a mixed-crystal state, prepared from a mixtureselectively comprising a plurality of chlorides, bromides, and iodidesof titanium, silicon, and aluminum with an arbitrary composition ratio,the production process and the use thereof.

BACKGROUND ART

The fields of industrial application of the ultrafine oxides have beenexpanding considerably in recent years. For instance, ultrafine titaniumoxide is being extensively studied as an ultraviolet-shielding agent, anadditive for a silicone rubber, and a photocatalyst. In particular, theapplication for cosmetics attracts special attention due to theultraviolet shielding effect of ultrafine titanium oxide, and, in lightof the photocatalytic properties of the ultrafine titanium oxide, someattention is also being paid to the application for prevention offouling, sterilization, and deodorizing. Such applications are supportedby the advantages of ultrafine titanium oxide in terms of safety,processability, functional characteristics, and durability. Theultrafine particles have not been exactly defined, but are generallyregarded as fine particles with a primary particle diameter of about 0.1μm or less.

The specific functions of titanium oxide, that is, scattering andabsorption of ultraviolet light, are noteworthy. It is more noticeablethat ultrafine particles of titanium oxide are favorably provided withthe above-mentioned two functions in combination. For instance,ultrafine titanium oxide with a primary particle diameter of about 80 nmcan work to effectively scatter ultraviolet light. In addition, it isknown that such ultrafine particles of titanium oxide can effectivelyabsorb ultraviolet light with a wavelength of about 400 nm or less andbe excited to generate electrons and/or holes in the portion adjacent tothe surface of the particle, thereby exhibiting such photocatalyticperformance as to carry out the prevention of fouling, sterilization,and deodorizing, as mentioned above.

However, when titanium oxide having such functions is used for cosmeticapplications in practice, there is the possibility that the titaniumoxide works improperly unless subjected to a surface treatment(coating). This is because the electrons and holes caused byphoto-excitation generate various radicals when allowed to react withoxygen and water in the air, so that they work to decompose organicmaterials in the air.

Titanium oxide is also used as a high-performance dielectric material.For example, titanium oxide is subjected to a solid phase reaction withbarium carbonate at 1,200° C. in accordance with the following reactionformula, thereby providing barium titanate serving as a dielectricmaterial.BaCO₃+TiO₂→BaTiO₃+CO₂

In this case, barium carbonate decomposes at around 700° C. to generateBaO with high tendency of ionization, which is diffused into TiO₂particles with covalent bonding characteristics to form a solidsolution, thereby producing barium titanate. The particle size of thebarium titanate is determined by the crystalline size of the TiO₂ in thecourse of the reaction. Therefore, the crystallinity and the particlesize of the titanium oxide serving as the raw material becomesignificant. To cope with the requirement for a small-size ceramiccondenser with a high dielectric constant, there is an increasing demandfor ultrafine particles of barium titanate, and consequently, forultrafine particles of titanium oxide as a raw material.

However, the growth of titanium oxide particles with a particle size of0.1 μm or less is striking at the above-mentioned reaction temperatureof about 700° C., so that there is the problem that such titanium oxideparticles cannot contribute to the provision of ultrafine particles ofbarium titanate. Ultrafine particles of titanium oxide for achieving theabove-mentioned object is desired.

As an example of a method for producing fine particles of a compositecontaining titanium oxide, a production process is known forfinely-divided particles of silica—titania composite material, that is,a production process of allowing a mixture of gaseous halogenatedsilicon and gaseous halogenated titanium to react with oxidizing gascontaining an oxygen at 900° C. or more (Japanese Laid-Open PatentApplication No. 50-115190). According to this method, the mixture ofgases serving as the raw material is subjected to a reaction underconditions of a high temperature of 900° C. or more without preheating.The resultant composite particles have such a structure that crystallineTiO₂ particles are always deposited on the surface of the compositeparticles.

Japanese Patent No. 2503370 (European Patent No. 595078) discloses thata mixed oxide of titanium oxide, aluminum oxide, and silicon oxide canbe produced by flame hydrolysis (at a reaction temperature of 1000 to3000° C.) using chlorides as raw materials. The flame hydrolysisproduces a mixed oxide of Al₂O₃ and TiO₂, or a mixed oxide of SiO₂ andTiO₂. Similarly, Japanese Patent No. 2533067 (European Patent No.585544) discloses manufacture of a mixed oxide of aluminum oxide andsilicon oxide by flame hydrolysis.

As previously mentioned, the production process for a metal oxide by avapor phase method, or the production process for a metal oxide or mixedmetal oxide by flame hydrolysis is conventionally known. However, thegrowing mechanism of the product particles that is, in general,seriously influenced by the reaction temperature, the gas flow velocity,the cooling rate, or the like, has not been sufficiently clarified.

DISCLOSURE OF THE INVENTION

In light of the applications of the previously mentioned ultrafine metaloxides, objects of the present invention are to provide a convenientproduction process for a surface-modified ultrafine mixed-crystal oxide,and to provide the ultrafine mixed-crystal oxide obtained by theprocess.

The inventors of the present invention have conducted an intensiveinvestigation in view of the prior art. As a result, the above-mentionedproblems were solved by producing an ultrafine mixed-crystal oxidecomprising primary particles with a mixed crystal state having a BETspecific surface area of about 10 to about 200 m²/g in such a mannerthat a mixed gas (hereinafter referred to as “a mixed halogenated metalgas”) comprising at least two compounds selected from the groupconsisting of chlorides, bromides, and iodides of titanium, silicon (Inthe present invention, silicon element is grouped together with a metalelement), and aluminum and an oxidizing gas are independently preheatedto about 500° C. or more prior to a reaction.

Namely, the present invention provides:

(1) a process for producing an ultrafine mixed-crystal oxidecharacterized by producing an ultrafine mixed-crystal oxide comprisingprimary particles in a mixed crystal state with a BET specific surfacearea of about 10 to about 200 m²/g, comprising the step of subjecting ahalogenated metal to high temperature oxidation with an oxidizing gas toproduce a metal oxide by a vapor phase production method, wherein thehalogenated metal is in the form of a mixed gas (a mixed halogenatedmetal gas) comprising at least two compounds each having a differentmetal element selected from the group consisting of chlorides, bromides,and iodides of titanium, silicon, and aluminum, and the mixedhalogenated metal gas and the oxidizing gas are independently preheatedto about 500° C. or more prior to a reaction;

(2) the production process of the ultrafine mixed-crystal oxideaccording to the aforementioned item (1), wherein the mixed halogenatedmetal gas is prepared by independently vaporizing at least two compoundseach having a different metal element selected from the group consistingof chlorides, bromides, and iodides of titanium, silicon, and aluminum,and mixing the compounds in a gaseous state;

(3) the production process of the ultrafine mixed-crystal oxideaccording to the aforementioned item (1) or (2), wherein the groupconsisting of chlorides, bromides, and iodides of titanium, silicon, andaluminum consists of TiCl₂, TiCl₃, TiCl₄, TiBr₃, TiBr₄, SiCl₄, Si₂Cl₆,Si₃Cl₈, Si₃Cl₁₀, Si₅Cl₁₂, Si₁₀Cl₁₂, SiBr₄, Si₂Br₆, Si₃Br₈, Si₄Br₁₀,SiI₄, Si₂I₆, SiCl₂I₂, SiClI₃, SiBr₃I, SiHI₃, SiCl₃I, SiH₃Br, SiH₂Br₂,SiHBr₃, SiCl₃Br, SiCl₂Br₂, SiClBr₃, AlCl₃, AlBr₃, and AlI₃;

(4) the production process of the ultrafine mixed-crystal oxideaccording to the aforementioned item (1), wherein the mixed halogenatedmetal gas and the oxidizing gas which are independently preheated toabout 500° C. or more are separately supplied to a reaction tube at aflow velocity of about 10 m/sec or more to carry out the reaction;

(5) the production process of the ultrafine mixed-crystal oxideaccording to the aforementioned item (1), wherein the reaction iscarried out with the mixed halogenated metal gas and the oxidizing gasbeing retained in the reaction tube for about 1 second or less under thecondition that the temperature in the reaction tube exceeds about 600°C.;

(6) the production process of the ultrafine mixed-crystal oxideaccording to the aforementioned item (1), wherein the gases in thereaction tube have an average flow velocity of about 5 m/sec or more;

(7) the production process of the ultrafine mixed-crystal oxideaccording to the aforementioned item (1), wherein the preheated mixedhalogenated metal gas and oxidizing gas cause turbulent flow whensupplied to the reaction tube;

(8) the production process of the ultrafine mixed-crystal oxideaccording to the aforementioned item (1) or (4), wherein the mixedhalogenated metal gas and the oxidizing gas are supplied to the reactiontube through a coaxial parallel flow nozzle which has an internal tubewith an inner diameter of about 50 mm or less;

(9) the production process of the ultrafine mixed-crystal oxideaccording to the aforementioned item (1), wherein a concentration of theaforementioned mixed halogenated metal gas is in a range of about 10 to100% by volume;

(10) the production process of the ultrafine mixed-crystal oxideaccording to the aforementioned item (1) or (4), wherein theaforementioned mixed halogenated metal gas and oxidizing gas arepreheated to about 800° C. or more;

(11) an ultrafine mixed-crystal oxide produced by the process accordingto the aforementioned item (1);

(12) the ultrafine mixed-crystal oxide as described in theaforementioned item (11), wherein the oxide has a BET specific surfacearea of about 10 to about 200 m²/g, and comprises primary particles witha mixed crystal having a titanium-oxygen-silicon bond;

(13) the ultrafine mixed-crystal oxide as described in theaforementioned item (11), wherein the oxide has a BET specific surfacearea of about 10 to about 200 m²/g, and comprises primary particles witha mixed crystal having a titanium-oxygen-aluminum bond;

(14) the ultrafine mixed-crystal oxide as described in theaforementioned item (12) or (13), wherein the oxide has a BET specificsurface area decreasing ratio of about 10% or less after heating atabout 800° C. for one hour;

(15) the ultrafine mixed-crystal oxide as described in theaforementioned item (12) or (13), wherein the oxide has a change inabsorbance of about 5 (/hr) or less when measured in such a manner thatthe oxide is dispersed at a concentration of 0.067% in a solvent of a98% glycerin in which Sunset Yellow is dissolved at a concentration of0.02%, thereby preparing a dispersion, and the dispersion is irradiatedwith a BLB lamp (ultraviolet light) with an intensity of 1.65 mW/cm² toobtain the change in absorbance (ΔOD) at 490 nm;

(16) the ultrafine mixed-crystal oxide as described in theaforementioned item (11), wherein the oxide has a BET specific surfacearea of about 10 to about 200 m²/g, and comprises primary particles witha mixed crystal having an aluminum-oxygen-silicon bond;

(17) the ultrafine mixed-crystal oxide as described in theaforementioned item (12), (13) or (16), wherein the oxide has an A/Bratio is about 0.001 or less when A is the content (%) of chlorine, andB is the BET specific surface area (m²/g);

(18) an ultrafine mixed-crystal oxide composition characterized bycomprising the ultrafine mixed-crystal oxides as described in theaforementioned item (11);

(19) an aqueous slurry characterized by comprising the ultrafinemixed-crystal oxide as described in the aforementioned item (11);

(20) an organic polymer composition characterized by comprising theultrafine mixed-crystal oxide as described in the aforementioned item(11);

(21) the organic polymer composition comprising the ultrafinemixed-crystal oxide as described in the aforementioned item (20),wherein an organic polymer in the organic polymer composition is atleast one kind of organic polymer selected from the group consisting ofa synthetic thermoplastic resin, a synthetic thermosetting resin, and anatural resin;

(22) the organic polymer composition comprising the ultrafinemixed-crystal oxide as described in the aforementioned item (20),wherein a concentration of the ultrafine mixed-crystal oxide in theorganic polymer composition is in a range of about 0.01 to about 80 mass% of total mass of the composite;

(23) a paint using the organic polymer composition as described in theaforementioned item (20);

(24) a compound using the organic polymer composition as described inthe aforementioned item (20);

(25) a master batch for a molded material selected from fiber, film, ormolded plastic, using the organic polymer composition comprising theultrafine mixed-crystal oxide in a high concentration as described inthe aforementioned item (20);

(26) a molded material characterized in that the molded material ismolded from the organic polymer composition comprising the ultrafinemixed-crystal oxide as described in the aforementioned item (20);

(27) the molded material as described in the aforementioned item (26),wherein the molded material is a fiber, a film, and a plastic moldedmaterial; and

(28) a structural material characterized by including, the ultrafinemixed-crystal oxide as described in the aforementioned item (11) on asurface of the structural material.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic diagram of one example of a reaction tube with acoaxial parallel flow nozzle, which tube is preferably used in thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be explained in detail.

The present invention relates to a process for producing an ultrafinemixed-crystal oxide characterized by producing an ultrafinemixed-crystal oxide comprising primary particles in a mixed crystalstate with a BET specific surface area of about 10 to about 200 m²/g,comprising the step of subjecting a halogenated metal to hightemperature oxidation with an oxidizing gas to produce a metal oxide bya vapor phase production method, wherein the halogenated metal is in theform of a mixed halogenated metal gas comprising at least two compoundshaving a different metal atoms selected from the group consisting ofchlorides, bromides, and iodides of titanium, silicon, and aluminum, andthe mixed halogenated metal gas and the oxidizing gas are independentlypreheated to about 500° C. or more prior to a reaction.

In the above-mentioned production process of the ultrafine mixed-crystaloxide, it is preferable that the mixed halogenated metal gas comprise atleast two compounds each having a different metal element selected fromthe group consisting of chlorides, bromides, and iodides of titanium,silicon, and aluminum. When the mixed halogenated metal gas is suppliedto a reaction tube, it is preferable that the halogenated metals beindependently vaporized into a gaseous state, followed by mixing in thegaseous state. As the oxidizing gas, oxygen, water vapor, or a mixed gascomprising oxygen and water vapor is used.

The chlorides, bromides, and iodides of titanium, silicon, and aluminumfor use in the present invention are not limited. Any halogenated metalthat can at least produce the corresponding halogenated metal gas whenpreheated to about 500° C. or more is usable. For example, TiCl₂, TiCl₃,TiCl₄, TiBr₃, TiBr₄, SiCl₄, Si₂Cl₆, Si₃Cl₈, Si₃Cl₁₀, Si₅Cl₁₂, Si₁₀Cl₁₂,SiBr₄, Si₂Br₆, Si₃Br₈, Si₄Br₁₀, SiI₄, Si₂I₆, SiCl₂I₂, SiClI₃, SiBr₃I,SiHI₃, SiCl₃I, SiH₃Br, SiH₂Br₂, SiHBr₃, SiCl₃Br, SiCl₂Br₂, SiClBr₃,AlCl₃, AlBr₃, and AlI₃ can be given as examples. Of these examples,TiCl₄, TiBr₄, SiCl₄, and AlCl₃ are particularly preferable.

In the present invention, the above-mentioned mixed halogenated metalgas and oxidizing gas are required to be independently preheated to atleast about 500° C. or more, preferably about 800° C. or more before thereaction. When the preheating temperatures of the mixed halogenatedmetal gas and the oxidizing gas are lower than about 500° C., uniformnucleation is decreased, and the reactivity is reduced. Therefore, it isdifficult to produce ultrafine particles, and the residual content ofchlorine is increased after dechlorination.

In the present invention, it is desirable that the mixed halogenatedmetal gas and the oxidizing gas be separately supplied to a reactiontube at a flow velocity of about 10 m/sec or more, more preferably about30 m/sec or more. In addition, it is preferable to carry out thereaction of these gases in such a manner that the gases are retained inthe reaction tube under the condition of high temperatures of about 600°C. or more to have a reaction time (which will also be hereinafterreferred to as “high-temperature residence time”) of about 1 second orless.

The inventors of the present invention have intensively studied thegrowing mechanism of particles in the vapor phase method. As a result,an oxide can be favorably obtained in the form of ultrafine particles bycontrolling both growing stages of the chemical vapor deposition (CVD)growing mechanism and the particle growing mechanism due to coalescenceof particles by collision and sintering which are factors having aneffect on the particle growth, to be curtailed. In other words, withrespect to the former factor for growth, the growth of an oxide can becontrolled when the chemical reactivity (reaction rate) is enhanced byelevating the preheating temperature. Concerning the latter factor forparticle growth, the growth caused by sintering or the like can beinhibited when the high-temperature residence time is minimized by rapidcooling and diluting after completion of the CVD. Under such productionconditions, an ultrafine mixed-crystal oxide with a BET specific surfacearea of about 10 to about 200 m²/g, preferably about 10 to about 100m²/g, can be obtained.

It is preferable that the flow velocities of the mixed halogenated metalgas and the oxidizing gas be about 10 m/sec or more when the gases areintroduced into the reaction tube. This is because the mixing of gasescan be promoted by increasing the flow velocities. When the gases havetemperatures of about 500° C. or more on entering the reaction tube, thereaction is completed simultaneously with the mixing step, so thatuniform nucleation is promoted. In addition, it is possible to curtailthe CVD-governed particle growing zone.

In the present invention, it is preferable that the material gas beintroduced into the reaction tube in a condition that the gasesintroduced there are thoroughly mixed. As long as the gases aresufficiently mixed, the fluid state of gas in the reaction tube is notparticularly limited. For example, a fluid state capable of causingturbulent flow is preferable. There may exist a spiral flow.

In the present invention, once the gases are supplied to the reactiontube, the larger the flow velocities of the gases in the reaction tubethe better in order to perfectly mix the gases. In particular, it ispreferable that the average flow velocity be about 5 m/sec or more. Whenthe flow velocity of each gas in the reaction tube is about 5 m/sec ormore, the gases can be thoroughly mixed in the reaction tube.

As a nozzle for introducing the material gas into the reaction tube,nozzles that can provide a coaxial parallel flow, oblique flow, or crossflow are employed, but not limited thereto. In general, the coaxialparallel flow nozzle is preferably employed from the viewpoint of designbecause the structure thereof is simpler although the coaxial parallelflow nozzle is inferior to other nozzles that can provide oblique flowor cross flow in terms of mixing performance. For example, when thecoaxial parallel flow nozzle is employed, a chloride-containing-gas isintroduced into the internal tube, and the oxidizing gas is introducedinto the external tube. In this case, it is preferable that the internaltube have a diameter of about 50 mm or less, and more preferably about50 mm to about 10 mm, from the viewpoint of mixing of gases.

The reaction in the reaction tube is an exothermic reaction, and thereaction temperature is higher than the sintering temperature for theresulting ultrafine titanium oxide. Although heat is lost by radiationfrom the reaction vessel, sintering of the resulting ultrafine particlesproceeds to promote particle growth unless the reaction product israpidly cooled after the reaction. In the present invention, it ispreferable to set the high-temperature residence time at about 600° C.or more in the reaction tube to about 1 second or less, followed byrapid cooling.

To rapidly cool the particles after the reaction, there are the methodsof introducing large quantities of cooling air or nitrogen gas or thelike into the reaction mixture after the reaction, and of spraying waterthereto.

FIG. 1 is a schematic diagram of a reaction tube provided with a coaxialparallel flow nozzle used for the production of the ultrafinemixed-crystal oxide according to the present invention. A mixedhalogenated metal gas is preheated to a predetermined temperature in apreheater 2, and introduced into a reaction tube 3 through an internaltube of a coaxial parallel flow nozzle 1. An oxidizing gas is preheatedto a predetermined temperature in a preheater 2, and introduced into thereaction tube 3 through an external tube of the coaxial parallel flownozzle 1. The gases introduced into the reaction tube are mixed to carryout the reaction. After that, the mixed gases are rapidly cooled with acooling gas, and sent to a bag filter 4 to collect the ultrafinemixed-crystal oxide particles.

The material gas may be made of 100% by volume of the above-mentionedmixed halogenated metal gas. Alternatively, the mixed halogenated metalgas may be diluted with an inert gas to have a concentration of about 10vol. % or more and less than 100%, preferably a concentration of about20 vol. % or more and less than 100 vol. %. When the material gascomprises the mixed halogenated metal gas at a concentration (a totalconcentration of halogenated metal gas) of about 10 vol. % or more,uniform nucleation can be increased and the reactivity is enhanced. Asthe above-mentioned inert gas, any inert gas that is not reactive withthe mixed halogenated metal and is not oxidized may be selected. Morespecifically, nitrogen and argon are preferable diluent gases.

The ultrafine mixed-crystal oxide obtained by the production processaccording to the present invention will now be explained. The ultrafinemixed-crystal oxide of the present invention has a BET specific surfacearea of about 10 to about 200 m²/g. In the case where at least two kindsof compounds containing titanium and silicon are used for the mixedhalogenated metal gas serving as the raw material in the productionprocess of the present invention, there can be obtained an ultrafinemixed-crystal oxide comprising primary particles in a mixed crystalstate with a titanium-oxygen-silicon bond. The above-mentioned ultrafinemixed-crystal oxide has an average primary particle diameter of about0.008 to about 0.1 μm, preferably about 0.015 to about 0.1 μm.

The BET specific surface area decreasing ratio obtained after heatingwas evaluated as an indication of the resistance to sintering propertiesof the ultrafine mixed-crystal oxide (the measuring method is describedlater). As a result, the ultrafine mixed-crystal oxide comprising theabove-mentioned titanium-oxygen-silicon bond has the characteristic thatthe BET specific surface area decreasing ratio is about 10% or lessafter the oxide is heated at about 800° C. for one hour.

With respect to the ultrafine mixed-crystal oxide of the presentinvention, when at least two kinds of compounds containing an element oftitanium and aluminum are used for the mixed halogenated metal gasserving as the raw material, an ultrafine mixed-crystal oxide comprisingprimary particles in a mixed crystal state with atitanium-oxygen-aluminum bond can be obtained. In this case, theultrafine mixed-crystal oxide comprising the above-mentionedtitanium-oxygen-aluminum bond has the characteristic that the BETspecific surface area decreasing ratio is 10% or less after the oxide isheated at about 800° C. for one hour.

Further, with respect to the ultrafine mixed-crystal oxide of thepresent invention, when at least two kinds of compounds containingaluminum and silicon are used for the mixed halogenated metal gasserving as the raw material, an ultrafine mixed-crystal oxide comprisingprimary particles in a mixed crystal state with analuminum-oxygen-silicon bond can be obtained. In this case, theultrafine mixed-crystal oxide comprising the above-mentionedaluminum-oxygen-silicon bond has the characteristic that the BETspecific surface area decreasing ratio is about 10% or less after theoxide is heated at about 800° C. for one hour.

As an indication of photo-activity of the ultrafine mixed-crystal oxideaccording to the present invention, the ultrafine mixed-crystal oxide(for example, comprising primary particles in a mixed-crystal state withthe titanium-oxygen-silicon bond, titanium-oxygen-aluminum bond, orsilicon-oxygen-aluminum bond) were characterized with regard to thedecreasing rate of dye absorbance under ultraviolet light irradiation.As a result, the ultrafine mixed-crystal oxide of the present inventionis characterized by a change in absorbance of about 5 (/hr) or less whenmeasured in such a manner that Sunset Yellow (dye) is dissolved at aconcentration of 0.02% and the oxide is dispersed at a concentration of0.067% in a solvent of a 98% glycerin, and the resultant dispersion isirradiated with a BLB lamp (ultraviolet light lamp) with an intensity of1.65 mW/cm² to obtain the change in absorbance (ΔOD) at 490 nm.

In addition, it is surprisingly confirmed that the content of chlorineremaining in the oxide obtained after a dechlorination step is extremelylow when silicon oxide exists in the oxide, as compared with the casewhere the oxide comprises no silicon oxide.

According to the present invention, in the ultrafine mixed-crystal oxidein a mixed-crystal state having any of the above-mentioned bonds, it ispreferable that the A/B ratio be about 0.001 or less when A is thecontent (%) of chlorine, and B is the BET specific surface area (m²/g).

The ultrafine mixed-crystal oxide obtained by the production process ofthe present invention may have a core/shell structure, which ispreferably made of a crystalline compounded structure comprisingdifferent metal oxides. For instance, there are observed a TiO₂-richphase in the core, and a SiO₂-rich phase in the shell in atitanium-silicon based ultrafine mixed-crystal oxide comprising theprimary particle in a mixed-crystal state having atitanium-oxygen-silicon bond.

The ultrafine mixed-crystal oxide of the present invention can be usedas a pigment, a dielectric raw material or an additive in cosmetics andclothing, and as an ultraviolet shielding agent and an abrasive in avariety of compositions such as silicone rubber and paper. Atitanium-containing silicon or aluminum based mixed-crystal oxide can beused as a photocatalytic powder with a controlled photocatalytic effect.This is because such an oxide can reduce or magnify the photocatalyticproperties peculiar to titanium oxide.

The aqueous slurry of the present invention means aqueous dispersantcomprising the ultrafine mixed-crystal oxide. No particular limitationis imposed on an amount of the ultrafine mixed-crystal oxide containedin said slurry. For example, the amount is preferable to be in a rangeof about 0.01 to about 50 mass %, more preferably about 1 to about 40mass %. When the amount of the ultrafine mixed-crystal oxide containedin the slurry is less than about 0.01 mass %, sufficient properties ofthe ultrafine mixed-crystal oxide can not be obtained. On the other handwhen the amount of the ultrafine mixed-crystal oxide contained in theslurry is more than about 50 mass %, it results in arising problems ofincreasing viscosity and economical disadvantage.

To this aqueous dispersant (slurry), arbitrary amount of binder is addedto produce a coating agent. A structural material containing theultrafine mixed-crystal oxide on its surface is produced by painting thecoating agent on a surface of various structural materials describedlater. In the present invention, no particular limitation is imposed onthe binder material, both organic and inorganic binder can be preferablyused. Specific examples of the organic binder include poly(vinylalcohol), melamine resin, urethane resin, celluloid, chitin, starchsheet, polyacrylamide, and acrylamide. Examples of the inorganic binderinclude zirconium compound such as zirconium oxychloride, zirconiumhydroxychloride, zirconium nitrate, zirconium sulfate, zirconiumacetate, zirconium ammonium carbonate, zirconium propionate; siliconcompound such as silane alkoxide, silicate; and metal alkoxide such asaluminum alkoxide, titanium alkoxide.

The amount of the binder added in the coating agent, for example, ispreferably in a range of about 0.01 to about 20 mass %, more preferablyabout 1 to about 10 mass %. When the binder content is less than about0.01 mass %, sufficient adhesive property after coating treatment cannot be obtained. When the binder content is more than about 20 mass %,it results in arising problems of increasing viscosity and economicaldisadvantage.

The ultrafine mixed-crystal oxide of the present invention can be addedin a organic polymer to produce a composition for use. The organicpolymer to be used includes a synthetic thermoplastic resin, a syntheticthermosetting resin, and a natural resin etc. Specific examples of theorganic polymer include polyolefin such as polyethylene, polypropylene,and polystyrene; polyamide such as nylon 6, nylon 66, and aramid;polyester such as polyethylene terephthalate, and unsaturated polyester;polyvinylchloride, polyvinylidene chloride, polyethylene oxide,polyethylene glycol, silicon resin, poly(vinyl alcohol), vinyl acetalresin, polyacetate, ABS resin, epoxy resin, vinyl acetate resin,cellulose and cellulose derivatives such as rayon, urethane resin,polyurethane resin, polycarbonate resin, urea resin, fluororesin,poly(vinylidene fluoride), phenol resin, cellulloid, chitin, starchsheet, acryl resin, melamine resin, alkyd resin.

The organic polymer composition containing the ultrafine mixed-crystaloxide of the present invention can be used as a paint(coatingcomposition), a compound, and a masterbatch. A concentration of theultrafine mixed-crystal oxide in the organic polymer composition basedon a total mass of said composition is preferably about 0.01 to about 80mass %, more preferably about 1 to about 50 mass %.

In the present invention, a molded material can be obtained by moldingthe above described polymer composition. The molded composition includefiber, film, and molded plastic.

Further, the organic polymer composition of the present invention havingsuperior durability can be used as a coating composition for astructural material such as a wall material, a glass, a signboard, and aconcrete for construction of the road. when the coating composition isapplied to structural materials(organic material) such as paper,plastics, fabric, and wood; or to vehicles, it can be free ofdeterioration or defect of the coating.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will now be explained in more detail withreference to the following examples, but the present invention is notparticularly limited by these examples.

<Evaluation of Resistance to Sintering Properties>

The BET specific surface area decreasing ratio after heating the oxidewas determined as an indication of the resistance to sinteringproperties of the ultrafine mixed-crystal oxide according to the presentinvention.

1 g of a raw material powder was placed in an aluminum crucible andheated at 800° C. for one hour in a siliconit furnace. After the powderwas cooled to room temperature, the BET specific surface area wasmeasured. When the BET specific surface area of the raw material powderis represented by B1 (m²/g) and the BET specific surface area afterheating is represented by B2 (m²/g), the BET specific surface areadecreasing ratio is defined in accordance with the following formula:BET specific surface area decreasing ratio={1−(B2/B1)}×100 (%)

The smaller the BET specific surface area decreasing ratio, the superiorthe resistance to the sintering properties to be evaluated.

<Evaluation of Photo-Activity>

To evaluate the photo-activity of the ultrafine mixed-crystal oxideaccording to the present invention, the dye absorbance decreasing rateby ultraviolet irradiation was employed as an indication.

In a 98% glycerin serving as a solvent, Sunset Yellow (azo dye) wasdissolved at a concentration of 0.02% and the oxide was dispersed at aconcentration of 0.067%. The resultant dispersion was placed in a quartzglass cell, and irradiated with a BLB lamp (ultraviolet lamp) with anintensity of 1.65 mW/cm². The absorbance at 490 nm was measured atregular intervals, and the decreasing rate, ΔOD, (unit: per hour) wasobtained. As the value of ΔOD becomes smaller, the photo-activity isconsidered to be more restrained.

<Evaluation of Mixed-Crystal State>

To identify the mixed-crystal state in the present invention, X-rayphotoelectron spectrometry (XPS) is employed. The details are referredto in A.Yu.Stakheev et al, J.Phys. Chem., 97(21), 5668–5672 (1993).

EXAMPLE 1

9.4 Nm³/hour (“N” means standard conditions, and the same meaningapplies correspondingly to the following) of gaseous titaniumtetrachloride with a concentration of 100 vol. %, and 2.4 Nm³/hour ofgaseous silicon tetrachloride with a concentration of 100 vol. % weremixed to prepare a material gas, and preheated to 1000° C. A mixed gasof 8 Nm³/hour of oxygen and 20 Nm³/hour of water vapor was preheated to1000° C. Both the material gas and the mixed gas were introduced into areaction tube at respective flow velocities of 49 m/sec and 60 m/sec,using a coaxial parallel flow nozzle. For the reaction, a reaction tubesuch as shown in FIG. 1 was employed, which reaction tube was providedwith a coaxial parallel flow nozzle having an internal tube with adiameter of 20 mm. The mixed halogenated metal containing gas wasintroduced through the internal tube.

The inner diameter of the reaction tube was 100 mm, and the countedvalue of the flow velocity in the tube at the reaction temperature of1,300° C. was 10 m/sec. Cooling air was introduced into the reactiontube after the reaction so that the high-temperature residence time inthe reaction tube was 0.3 sec or less. Thereafter, the producedultrafine particles were collected using a Teflon bag filter. Theultrafine particles were then heated at 500° C. for one hour underatmospheric conditions using an oven, thereby performing adechlorination process.

With respect to the obtained ultrafine mixed-crystal oxide, the BETspecific surface area was 88 m²/g, the average true specific gravity was3.7 g/cc, the average primary particle diameter was 0.018 μm, and theresidual content of chlorine was 0.01%. The titanium-oxygen-silicon bondwas apparently confirmed by the XPS.

In addition, the photo-activity (hereinafter referred to as “ΔOD”) was0.1/hr, the BET specific surface area decreasing ratio after completionof the heating at 800° C. for one hour (hereinafter referred to as “ΔB”)was 2%, and the ratio of the chlorine content to the BET specificsurface area (hereinafter referred to as “A/B”) was 0.0001.

EXAMPLE 2

8.3 Nm³/hour of gaseous titanium tetrachloride, 2.4 Nm³/hour of gaseousaluminum trichloride, and 6 Nm³/hour of nitrogen were mixed to prepare amaterial gas, and preheated to 900° C. A mixed gas of 8 Nm³/hour ofoxygen and 20 Nm³/hour of water vapor was preheated to 1000° C. Both thematerial gas and the mixed gas were introduced into a reaction tube atrespective flow velocities of 63 m/sec and 60 m/sec, using a coaxialparallel flow nozzle. For the reaction, a reaction tube such as shown inFIG. 1 was employed, which reaction tube was provided with a coaxialparallel flow nozzle having an internal tube with a diameter of 20 mm.The gas containing mixed halogenated metal was introduced through theinternal tube.

The inner diameter of the reaction tube was 100 mm, and the countedvalue of the flow velocity in the tube at the reaction temperature of1,200° C. was 10 m/sec. Cooling air was introduced into the reactiontube after the reaction so that the high-temperature residence time inthe reaction tube was 0.3 sec or less. Thereafter, the producedultrafine particles were collected using a Teflon bag filter. Theultrafine particles were then heated at 500° C. for one hour underatmospheric conditions using an oven, thereby performing adechlorination process.

With respect to the obtained ultrafine mixed-crystal oxide, the BETspecific surface area was 48 m²/g, the average true specific gravity was3.9 g/cc, the average primary particle diameter was 0.032 μm, and theresidual content of chlorine was 0.1%. The titanium-oxygen-aluminum bondwas apparently confirmed by the XPS.

In addition, the value of ΔOD was 1.2/hr, the value of ΔB was 5%, andthe A/B ratio was 0.002.

EXAMPLE 3

1.2 Nm³/hour of gaseous silicon tetrachloride, 8.3 Nm³/hour of gaseousaluminum trichloride, and 10 Nm³/hour of nitrogen were mixed to preparea material gas, and preheated to 1,000° C. A mixed gas of 8 Nm³/hour ofoxygen and 20 Nm³/hour of water vapor was preheated to 1000° C. Both thematerial gas and the mixed gas were introduced into a reaction tube atrespective flow velocities of 80 m/sec and 60 m/sec, using a coaxialparallel flow nozzle. For the reaction, a reaction tube such as shown inFIG. 1 was employed, which reaction tube was provided with a coaxialparallel flow nozzle having an internal tube with a diameter of 20 mm.The gas containing mixed halogenated metal was introduced through theinternal tube.

The inner diameter of the reaction tube was 100 mm, and the countedvalue of the flow velocity in the tube at the reaction temperature of1,200° C. was 11 m/sec. Cooling air was introduced into the reactiontube after the reaction so that the high-temperature residence time inthe reaction tube was 0.3 sec or less. Thereafter, the producedultrafine particles were collected using a Teflon bag filter. Theultrafine particles were then heated at 500° C. for one hour underatmospheric conditions using an oven, thereby performing adechlorination process.

With respect to the obtained ultrafine mixed-crystal oxide, the BETspecific surface area was 120 m²/g, the average true specific gravitywas 3.5 g/cc, the average primary particle diameter was 0.014 μm, andthe residual content of chlorine was 0.004%. The silicon-oxygen-aluminumbond was apparently confirmed by the XPS.

In addition, the value of ΔB was 2%, and the A/B ratio was 0.00003.

COMPARATIVE EXAMPLE 1

10.7 Nm³/hour of gaseous titanium tetrachloride and 12 Nm³/hour ofnitrogen were mixed to prepare a material gas, and preheated to 900° C.A mixed gas of 8 Nm³/hour of oxygen and 20 Nm³/hour of water vapor waspreheated to 1000° C. Both the material gas and the mixed gas wereintroduced into a reaction tube at respective flow velocities of 86m/sec and 60 m/sec, using a coaxial parallel flow nozzle. For thereaction, a reaction tube such as shown in FIG. 1 was employed, whichreaction tube was provided with a coaxial parallel flow nozzle having aninternal tube with a diameter of 20 mm. The gas containing thehalogenated metal was introduced through the internal tube.

The inner diameter of the reaction tube was 100 mm, and the countedvalue of the flow velocity in the tube at the reaction temperature of1,200° C. was 12 m/sec. Cooling air was introduced into the reactiontube after the reaction so that the high-temperature residence time inthe reaction tube was 0.3 sec or less. Thereafter, the producedultrafine particles were collected using a Teflon bag filter. Theultrafine particles were then heated at 500° C. for one hour underatmospheric conditions using an oven, thereby performing adechlorination process.

With respect to the obtained ultrafine oxide, the BET specific surfacearea was 51 m²/g, the average true specific gravity was 4.0 g/cc, theaverage primary particle diameter was 0.029 μm, and the residual contentof chlorine was 0.4%.

In addition, the value of ΔOD was 21/hr, the value of ΔB was 62%, andthe A/B ratio was 0.007. This product is found to have higherphoto-activity, and to be more easily sintered when compared with theproducts produced in Examples 1 and 2. In addition, there remains muchamount of chlorine.

COMPARATIVE EXAMPLE 2

8.3 Nm³/hour of gaseous aluminum trichloride and 20 Nm³/hour of nitrogenwere mixed to prepare a material gas, and preheated to 1,000° C. A mixedgas of 8 Nm³/hour of oxygen and 20 Nm³/hour of water vapor was preheatedto 1,000° C. Both the material gas and the mixed gas were introducedinto a reaction tube at respective flow velocities of 107 m/sec and 60m/sec, using a coaxial parallel flow nozzle. For the reaction, areaction tube such as shown in FIG. 1 was employed, which reaction tubewas provided with a coaxial parallel flow nozzle having an internal tubewith a diameter of 20 mm. The gas containing the halogenated metal wasintroduced through the internal tube.

The inner diameter of the reaction tube was 100 mm, and the countedvalue of the flow velocity in the tube at the reaction temperature of1,200° C. was 12 m/sec. Cooling air was introduced into the reactiontube after the reaction so that the high-temperature residence time inthe reaction tube was 0.3 sec or less. Thereafter, the producedultrafine particles were collected using a Teflon bag filter. Theultrafine particles were then heated at 500° C. for one hour underatmospheric conditions using an oven, thereby performing adechlorination process.

With respect to the obtained ultrafine oxide, the BET specific surfacearea was 115 m²/g, the average true specific gravity was 3.7 g/cc, theaverage primary particle diameter was 0.014 μm, and the residual contentof chlorine was 0.5%.

In addition, the value of ΔB was 7%, and the A/B ratio was 0.004.

This product is found to be more easily sintered and there remains moreamount of chlorine when compared with the product produced in Example 3.

EXAMPLE 4

Water is added to the ultrafine mixed-crystal oxide having atitanium-oxygen-silicon bond obtained in example 1, to produce a slurrycontaining 0.5 mass % of the oxide on the solid powder basis. To theslurry, an aqueous dispersed urethane resin (VONDIC1040NS, produced byDAINIPPON INK AND CHEMICALS, INCORPORATED.) is added to produce acoating agent containing urethane resin by 70 mass % on the solid powderbasis and photo-functional powder.

The obtained coating agent is painted on one side of polyethyleneterephthalate(PET) film (100 μm Lumilar T, produced by Toray Industries,Inc) by an applicator(25 μ□). And the resulting film is dried at 80□ fortwo hours to produce a polyethylene terephthalate film including theultrafine mixed-crystal oxide.

A percent transmission of the obtained polyethylene terephthalate filmis measured by spectrometer(UV-2400PC, produced by Shimazu Co., Ltd) tobe 1% (360 nm) and 89% (550 nm).

A light resistance test is conducted to the above described polyethyleneterephthalate film by applying a light of 76 mW/cm² using fademeter(SUNSET CPS+, produced by Heraeus), and coloring of the film after 100hours is investigated. No coloring is observed.

EXAMPLE 5

20 mass parts of the ultrafine mixed-crystal oxide having atitanium-oxygen-silicon bond obtained in example 1, 2 mass parts of zincstearate (zinc stearate S, produced by NOF CORPORATION), 78 mass partsof low density polyethylene (LDPE) (JAPAN POLYOLEFINS CO., Ltd.) ismelt-kneaded at 160□ (residence time is about 3 minutes) using biaxialextruder (PCM type 30, produced by Ikegai tekkou Co., Ltd.), and foamedto pellet, to produce 20 kg of a cylinder shaped compound of low densitypolyethylene having a diameter of 2˜3 mmφ, a length of 3˜5 mm, and aweight of 0.01˜0.02 g, containing 20% of the ultrafine mixed-crystaloxide.

1 kg of the obtained compound of low density polyethylene containing theultrafine mixed-crystal oxide and 39 kg of low density polyethlene(LDPE) (JAPAN POLYOLEFINS CO., Ltd.) are mixed using V-typeblender(RKI-40, produced by IKEMOTO SCIENTIFIC TECHNOLOGY CO., LTD) for10 minutes to produce a mixed pellet.

The obtained mixed pellet is molded using inflation film molding machineequipped with 40 mmφof extruder (YEI-S40-40L, produced by YOSHIITEKKOUCO., LTD) to produce 40 μ□ of inflation film. Transmission and lightresistance tests are conducted to the obtained film in the sameprocedure as in example 4. The results obtained are shown in Table 1below.

COMPARATIVE EXAMPLE 3

A purchased ultrafine titanium dioxide (ST-01, produced by ISHIHARAINDUSTRIES CO., LTD.) is treated and tested in the same procedure as inexample 4. The results obtained are shown in Table 1 below.

COMPARATIVE EXAMPLE 4

A purchased ultrafine titanium dioxide (ST-01, produced by ISHIHARAINDUSTRIES CO., LTD.) is treated and tested in the same procedure as inexample 4. The results obtained are shown in Table 1 below.

TABLE 1 Light % trans- % trans- resistance mission mission AdditivesApplication test (350 nm) (550 nm) Example 4 Ultrafine Painting on No 1% 89% mixed-crystal PET film coloring oxide containingtitanium-oxygen- silicon bond Example 5 Ultrafine LDPE inflation No  0%78% mixed-crystal film coloring oxide containing titanium-oxygen-silicon bond Comparative Ultrafine Painting on Coloring  3% 95% Example3 titanium PET film dioxide Comparative Ultrafine LDPE inflationColoring 10% 60% Example 4 titanium film dioxide

INDUSTRIAL APPLICABILITY

As previously explained in detail, according to the present invention,there can be provided an ultrafine mixed-crystal oxide comprising theprimary particles in a mixed-crystal state, the oxide being in the formof ultrafine particles with excellent dispersion properties, and havinga BET specific surface area of 10 to 200 m²/g. This is because the gascontaining a mixture of halogenated metals and the oxidizing gas areindependently preheated to 500° C. or more prior to the reaction in thevapor phase method for producing an ultrafine mixed-crystal oxide bysubjecting the mixture of halogenated metals to high temperatureoxidation using the oxidizing gas.

Further, for example, the ultrafine mixed-crystal oxide of the presentinvention can moderate or control the photoactivity and the sinteringproperties thereof. The residual amount of chlorine can be drasticallydecreased. The step of disintegrating of the particles becomesunnecessary, or can be performed using extremely simple facilities ifthe step is necessary. The ultrafine mixed-crystal oxide can be producedvery conveniently. The process for producing an ultrafine mixed-crystaloxide of the present invention is useful for various industrialapplications.

1. A silicone rubber or paper comprising an ultrafine mixed-crystaloxide characterized in that the ultrafine mixed-crystal oxide comprisesprimary particles in a mixed crystal state with a BET specific surfacearea of about 10 to about 200 m²/g, and is produced by a processcomprising the step of subjecting a halogenated metal to hightemperature oxidation with an oxidizing gas to produce a metal oxide bya vapor phase production method, wherein said halogenated metal is inthe form of a material gas containing a mixed halogenated metal gascomprising at least two compounds each having a different metal elementselected from the group consisting of chlorides, bromides, and iodidesof titanium, silicon, and aluminum, and said mixed halogenated metal gasand said oxidizing gas are supplied into a reaction tube at a flowvelocity of 10 m/sec or more to react after each is independentlypreheated to about 500° C. or more prior to a reaction.
 2. A siliconerubber or paper according to claim 1, wherein said oxide has a BETspecific surface area of about 10 to about 200 m²/g, and comprisesprimary particles with a mixed crystal having a titanium-oxygen-siliconbond.
 3. A silicone rubber or paper according to claim 1, wherein saidoxide has a BET specific surface area of about 10 to about 200 m²/g, andcomprises primary particles with a mixed crystal having atitanium-oxygen-aluminum bond.
 4. A silicone rubber or paper accordingto claim 2 or 3, wherein said oxide has a BET specific surface areadecreasing ratio of about 10% or less after heated at about 800° C. forone hour.
 5. A silicone rubber or paper according to claim 2 or 3,wherein said oxide has a change in absorbance of about 5 (/hr) or lesswhen measured in such a manner that said oxide is dispersed at aconcentration of 0.067% in a solvent of a 98% glycerin in which SunsetYellow is dissolved at a concentration of 0.02%, thereby preparing adispersion, and said dispersion is irradiated with a BLB lamp(ultraviolet light) with an intensity of 1.65 mW/cm² to obtain saidchange in absorbance (ΔOD) at 490 nm.
 6. A silicone rubber or paperaccording to claim 1, wherein said oxide has a BET specific surface areaof about 10 to about 200 m²/g, and comprises primary particles with amixed crystal having an aluminum-oxygen-silicon bond.
 7. A siliconerubber or paper according to claim 2, 3, or 6, wherein said oxide has anA/B ratio of about 0.001 or less when A is the content (%) of chlorine,and B is said BET specific surface area (m²/g).
 8. A structural materialincluding on the surface thereof an ultrafine mixed-crystal oxidecharacterized in that the ultrafine mixed crystal oxide comprisesprimary particles in a mixed crystal state with the BET specific surfacearea of about 10 to about 200 m²/g, and is produced by a processcomprising the step of subjecting a halogenated metal to hightemperature oxidation with an oxidizing gas to produce a metal oxide bya vapor phase production method, wherein said halogenated metal is inthe form of a material gas containing a mixed halogenated metal gascomprising at least two compounds each having a different metal elementselected form the group consisting of chlorides, bromides, and iodidesof titanium, silicon, and aluminum, and said mixed halogenated metal gasand said oxidizing gas are supplied into a reaction tube at a flowvelocity of 10 m/sec or more to react after each is independentlypreheated to about 500° C. or more prior to a reaction, wherein thestructural material comprises at least one selected from the group ofwall materials, glass, signboard, concrete for construction of the road,paper, plastic, fabric, wood, and materials for vehicles.
 9. Astructural material according to claim 8, wherein said oxide has a BETspecific surface area of about 10 to about 200 m²/g, and comprisesprimary particles with a mixed crystal having a titanium-oxygen-siliconbond.
 10. A structural material according to claim 8, wherein said oxidehas a BET specific surface area of about 10 to about 200 m²/g, andcomprises primary particles with a mixed crystal having atitanium-oxygen-aluminum bond.
 11. A structural material according toclaim 9 or 10, wherein said oxide has a BET specific surface areadecreasing ratio of about 10% or less after heated at about 800° C. forone hour.
 12. A structural material according to claim 9 or 10, whereinsaid oxide has a change in absorbance of about 5 (/hr) or less whenmeasured in such a manner that said oxide is dispersed at aconcentration of 0.067% in a solvent of a 98% glycerin in which SunsetYellow is dissolved at a concentration of 0.02%, thereby preparing adispersion, and said dispersion is irradiated with a BLB lamp(ultraviolet light) with an intensity of 1.65 mW/cm² to obtain saidchange in absorbance (ΔOD) at 490 nm.
 13. A structural materialaccording to claim 8, wherein said oxide has a BET specific surface areaof about 10 to about 200 m²/g, and comprises primary particles with amixed crystal having an aluminum-oxygen-silicon bond.
 14. A structuralmaterial according to claim 9, 10 or 13, wherein said oxide has an A/Bratio of about 0.001 or less when A is the content (%) of chlorine, andB is said BET specific surface area (m²/g).
 15. A structural materialincluding an ultrafine mixed-crystal oxide, wherein the ultrafinemixed-oxide comprises primary particles in a mixed crystal state with aBET specific surface area of about 10 to about 200 m²/g, and is producedby a process comprising the step of subjecting a halogenated metal tohigh temperature oxidation with an oxidizing gas to produce a metaloxide by a vapor phase production method, wherein said halogenated metalis in the form of a material gas containing a mixed halogenated metalgas comprising at least two compounds each having a different metalelement selected from the group consisting of chlorides, bromides, andiodides of titanium, silicon, and aluminum, and the said halogenatedmetal gas and said oxidizing gas are supplied into a reaction tube at aflow velocity of 10 m/sec or more to react after each is independentlypreheated to about 500° C. or more prior to a reaction, wherein thestructural material comprises at least one selected from the group ofwall materials, glass, signboard, concrete, paper, plastic, fabric,wood, and materials for vehicles.